From Iusmicm

Revision as of 23:16, 2 December 2011

Maternal-Fetal Physiology

Objectives

• List pertinent physiologic changes in various maternal systems
• Recognize that signs and symptoms in a pregnant patient are often more difficult to interpret
• Non-pregnant lab values and measurements are frequently abnormal in the pregnant state

Case: First Trimester

• 21 y/o G1P0 at 8w0d by L=6 week US at the WVC (women's visit center at Wishard) presents for her OB registration appointment.
  • She denies any LOF (leaking of fluid), VB (vaginal bleeding).
  • Pt with C/C of cramping and dark “poop”, nausea and vomiting with heart burn.
• PMH: Denied
• PSocialH: Denied
• OB: G1
• Gyn: Denied
• Social Hx: Denied x 3
• Allergies: NKDA
• Medications: PNV (Prenatal Vitamin)
• VS: BP: 110/80 P: 80 T: 98.6 Weight: 65Kg Height: 5’1
• UA: WNL
• PE: WNL

GI Issues in the First Trimester

• Constipation:
  • Iron (ferrous-sulfate) in the pre-natal vitamins slows GI motility and causes constipation.
  • Progesterone: a smooth muscle relaxant; causes decreased bowel movement which can lead to increased time for water reabsorption and thus constipation
  • Tx: give colace
  • Could be as bad a month!
  • There is fear of miscarriage throughout pregnancy so anything seeming abnormal (like not pooping) starts a fear of miscarriage.

• Nausea and Vomiting:
  • beta-HCG causes n/v
    • beta-HCG peaks at 10-12 weeks.
  • {rogesterone: a smooth muscle relaxant; causes decreased bowel movement which can lead to n / v.

• Weight gain:
  • can occur early or late, ideal is a progression.
  • vomitting can lead to weight loss over the first weeks, but mom and baby will be ok
  • Normal Weight for Height: about 20 lbs
  • Underweight Women: about 30 lbs
  • Overweight Women: about 16 lbs
  • Only an addition 300 calories / day are necessary to feed a fetus.
    • 500 cal for twins

Case: Second Trimester

• 21 y/o is now 20 weeks pregnant
• Presents to triage at Wishard with horrible heartburn after eating a deep fried twinkie at the state fair.
• She threw-up so much in early pregnancy that she is making up for it now.
  • She has gained 25 lbs (from 8 weeks to second trimester).
  • That is a lot of weight gain.
• She denied any LOF (leaking of fluid), denied VB (vaginal bleeding) or cramping.
• She stated that she had some of the chalkie things and it didn’t make it better this time.
  • Tums.
• She was given a GI cocktail in triage and she was still miserable.

• Differential Diagnosis:
  • Constipation
    • Small bowel obstruction
    • Ask when they last deficated.
  • Gallstones
    • Increased estrogen and progesterone
    • Slow emptying of the stomach
    • Often already at high risk (four "F"s: fat, forty, fertile, female)
    • Can look really, really, bad.
  • Pancreatitis
  • Appendicitis
    • Appendix moves from right lower quadrant to midquadrant
    • Can get tucked up behind the uterus

First / Second Trimester GI Presentations

• High levels of estrogen / progesterone in pregnancy lend themselves to gallstone formation
  • Especially when woman gets pregnant a second time without having gallstones from a previous pregnancy removed.

• Recall that progesterone is a smooth muscle relaxant.
• Recall that progesterone is at high levels throughout pregnancy to maintain the uterine environment.
  • Progesterone is really rampinig up during the first trimester.
• High circulating levels of progesterone can lead to:
  • Increased GERD from relaxation of GE sphincter
  • Constipation from delayed transit through large bowel
  • Increased N/V from delayed gastric emptying
  • Stomach can still be full of content 8 hours later.
  • “Full stomach” sensation

• Tx is often to keep pt from eating for 8 to 12 hours and then to switch to a little bit, throughout the day type consumption pattern.

Case: Second / Third Trimester

• 21 y/o G1P0 at 28w0d
• Presents to triage at St. Francis Beech Grove.
• Patient has been brought in by her family “Doc I feel horrible. I am dizzy. I was sitting at the high-school football game, I stood up to cheer, my heart started racing and I felt like I was going to pass-out! My ankles are swollen and I feel horrible."
• Denies LOF (leaking of fluid), VB (vaginal bleeding), CTXs (contractions).
• Endorses +FM (fetal movement).
• ED doctor noticed that she is breathing deeply.

• Pertinent Vitals:
  • BP: 100/60
  • P: 90
  • T: 98.6
  • RR: 16
  • O2: 96% RA
  • Weight: 80kgs

• Labs ordered:
  • CBC w/platelets
  • CXR (chest xray)
  • ABG (arterial blood gas)
  • UA (urinary analytes)
  • CMP (complete metabolic panel)
  • Coags (coagulation studies)

• PE:
  • Lungs: CTA B
  • CV: Systolic murmur
  • Abd: Gravid, NT
  • Extrem: +1 pitting edema

• Lab results:
  • WBC: 10,000 (slightly elevated)
  • Hgb / HCT: 10.5/31.7% (decrease)
  • Platelets: 200,000 (slight decrease)
  • Fibrinogen: 600 (increased)
  • Bun / Cr: 3 / 0.6 (decreased)
  • pH: 7.44
  • pCO2: 30
  • BiCarb: 21
  • paO2: 103

Physiological Changes in Pregnancy

Blood pressure in pregnancy

• Pt blood pressure: 100/60
• Both systolic and diastolic BP decrease in 2nd trimester
• Systalic decreases 5-10 mmHg
• Diastolic decreases 10-15 mmHg
• We even take severe hypertensive pts off their meds.
• Normal

• Monitor from baseline!
  • Athletes will have low baseline BP and therefore it will be a challenge to keep their BP up during pregnancy.

Pulse in pregnancy

• Pt's pulse: 90
• Increases 20 beats (peak at 32 weeks, middle of 3rd trimester)
• Normal

Cardiac output in pregnanc

• Recall that cardiac output (CO) is stroke volume (SV) multiplied by the heart rate (HR).
• CO increases at 8 weeks and peaks at 20 weeks.
• CO increases by 30-50%
• CO rises to 4.5-6.0 L / min

How do we know her stroke volume?

• Systolic ejection murmur is common (90% of women).
• S3 gallop is common (90% of women).
• Peripheral vascular resistance falls during pregnancy, too.
  • Hence the swelling.
  • Wear flipflops, wear compression socks
  • Especially medical residents.

Respiratory rate in pregnancy

• Recall your standard respiratory volumes (see image below).
• Note that O2 demand (consumption) is increased by 15-20% in pregnancy.
• These volumes are affected by the displacement of the diaphragm rostrally.
• Note that respiratory rate should remain unchanged in normal pregnancy.
  • This is possible because the tidal volume increases (because the minute ventilation increases).
• Functional residual capacity decreases by 20% because of displacement the uterus.

• So dyspnea is normal with pregnancy.

Arterial blood gas (ABG) in pregnancy

• NB: ABG should never be "normal" in pregnancy!
  • Should have a respiratory alkalosis from blowing off their CO2 at higher rates.
  • Should have a metabolic acidosis (compensatory).
• Many pregnant women will hyperventalate.
  • Give them a bag in which to breath.
  • Very hard to settle them down so important to give the bag quickly and pt will often become syncopous.

• Pt's ABG was:
  • pH: 7.44 (
  • pCO2: 30
  • BiCarb: 21
  • paO2: 103

• Recall that O2 consumption increases in pregnancy.
  • 15-20%
• Recall that minute ventilation (the amount of air breathed in over the course of one minute) is increased relatively more than the O2 consumption.
  • This means that more air is breathed in and out than is necessary for the rate of oxygen consumption.
  • This is the definition of hyperventilation!
• Recall the chemical equation: CO2 + H20 <=> H2CO3 <=> HCO3 + H
• Recall that hyperventilation gives off CO2, dragging the equation to the left.
  • That is, pCO2 will be decreased.
• Therefore pregnant, hyperventilating women become alkalotic (decreased H+).
  • That is, pH will be high (less H+).
  • This is a respiratory alkalosis.
• Recall that the kidneys can excrete HCO3 to compensate for loss of CO2 (because of hyperventilation) and thus draw the equation back to the right.
  • Thus we expect the serum HCO3 to be low.
• Recall that in pregnancy there is an increased oxygen carrying capacity (facilitated by RBC volume increased by 50%).
  • Thus we expect the pO2 to be high.

• Given this respiratory alkalosis and metabolic (compensatory) acidosis, we expect:
  • the pCO2 to be low: 26-32 mmHg (compared to non-pregnancy 38-45)
  • the pH to be high (alkaline): 7.40-7.46 (compared to non-pregnancy 7.38-7.42)
  • the HCO3 to be low: 18-21 mEq / L (compared to non-pregnancy 24-31)
  • the pO2 to be high: 106-108 mmHg (compared to non-pregnancy 70-100)

• A high pCO2 is cause for alarm in the asthmatic pregnant woman.
• Also, pCO2 should be monitored carefully in the acutely infected pregnant woman because they are immune compromised and have very little respiratory reserve.

• Importance:
  • A normal pregnant woman has a compensated respiratory alkalosis (with a compensatory metabloic acidosis) and a diminished pulmonary reserve.
• Cause:
  • Progesterone: relaxes the smooth muscle
  • Diaphragm raised 4cm

CBC in pregnancy

• Plasma Volume and RBC Mass
  • Plasma volume increases by about 50%
  • RBC volume increases by about 30%
• Result:
  • “Physiologic anemia of pregnancy”
  • The mean Hgb is about 11.5 g/dl
• At 28 weeks, get new labs.
• Will likely need to start iron.
  • Start at or below 10.
  • Yucky tasting, makes woman feel horrible.
  • Necessary for proper oxygenation.

Coagulation in pregnancy

• In pregnancy the pt is hypercoaguable
  • This is the body's way to not die from bleeding when the parasite is ejected / ripped from the internal surface of the uterus.
• DIC is the number 1 cause of death in laboring women around the world.
  • Not so much here in the US.
• Procoagulant’s are increased: I, VII, VIII, IX, X and Fibrinogen.
• Prevents Peripartum Hemorrhage
• Can lose 1500mL without blinking.
• Over 2000 mL lost, start worrying b/c coag factors are becoming deficient.

Renal System in pregnancy

• Bun & Serum Creatinine decreases by about 25%
  • Low because of increased blood volume, increased GFR, increased blood flow to the kidneys
• Plasma osmolarity decreases by about 10 mOsm / kg H20
• Increase in tubal reabsorption of sodium
• Marked increase in renin and angiotensin levels
  • But markedly reduced vascular sensitivity to their hypertensive effects
• Increased glucose excretion
  • Fine during labor, a coping mechanism.
  • Labs at 28 weeks detect gestational diabetes.

• Anatomic:
  • Kidney size increases
  • Kidney weight increases
  • Ureteral dilation (right side greater than left side)
    • Because of the angle of the uterus
  • Bladder becomes an intra-abdominal organ

• Hemodynamic:
  • GFR increase by 50%
  • Renal plasma increased by flow by 75%
  • Creatinine Clearance increases to 150-200 cc / min
    • Most important kidney function test in pregnancy

• Swollen Ankles:
  • Recall that the Plasma Volume Increases 50% in pregnancy.
  • Recall that there is decreased Systemic Vascular resistance in pregnancy.
  • Recall that there is renal retention of Na and H20 in pregnancy.
    • Leads to a total increase of 6 – 8 L in total body H20!
    • 2 / 3rd extracellular
    • 1 / 3rd intravascular
    • Intravascular increase is put in the "dependent" (affected by gravity) areas like the lower venous system.
  • Hard to move fluids through the venous system.

Case: Caring Family

• The patient’s husband lies her flat in an effort to keep her comfortable.
• The fetus’s FHTs (fetus heart tones) drop to 80.
• But, the ROCK STAR medical student wedges the patient quickly on her left side and the FHT’s recover quickly!
  • Turns her off the vena cava.
  • Aids in venous return to the heart and therefore to oxygenation of blood for mom and baby.

• What happened to the cared-for mother?
• Gravid Uterus placed pressure on the IVC which resulted in decreased “utero-placental blood flow.”
  • Cardiac output falls
  • Blood is shunted to the brain and
  • Blood is shunted away from the uterus and placenta
  • This causes a reflex fetal bradycardia

Importance of Physiology

• All can be abnormal in the Non-Pregnant state:
  • Decreased BP
  • Swollen ankles
  • CXR: cardiomegaly, leftward deviation
  • Systolic Ejection murmur
  • Dyspnea
  • Anemia
  • Hypercoaguable
  • NORMAL for Pregnancy

Maternal Physiology Review